Pressure compensated pump



Feb. 12, 1952 j K OUG S PRESSURE COMPENSATED PUMP 4 Sheets-Sheet 1 Filed March 27, 1950 FIG. 1'

INVENTOR JAMES K. DOUGLAS B WW ATTORNEY Feb. 12, 1952 J. K. DOUG LAS 2585232 PRESSURE COMPENSATED PUMP Filed March 27, 1950 4 Sheets-Sheet 2 3 6 3 7 v I I;

FIG. 2

INVENTOR JAMES K. DOUGLAS ATTORN-EY Feb. 12, 1952 .1. K. DOUGLAS PRESSURE COMPENSATED PUMP 4 Sheets-Sheet 3 Filed March 27, 1950 BRIDGE CENTER LlNE- I HORIZONTAL 3 CENTER LINE INVENTOR JAMES K. DOUGLAS 'BY 7% W ATTORNEY Patented Feb. 12, 1952 UNITE STATES ATENT OFFICE PRESSURECOMPENSATED PUMP- James K. Douglas, Shorewood, Wia, assignor to The Oilgear Company, Milwaukee, Wis.', "a corporation of Wisconsin Application March 2-7, 1950, Seria'l'No; 152,256

9 Claims. (01. 103-161) a This invention relates to variable displacement.

pumps of the type employed to deliverliqui'd'at closely regulated volumetric rates and it relatesmore particularly to a pump in whicha pluralityof-cylinders are arranged radially" in an inner rotor, a piston is fitted in each cylinderfthe inner rotor is journaled upon a valve shaft or pintle which controls the flow of liquid to andfromthe" cylinders, and an outer rotor is arranged around the-inner rotor in engagement with the outer ends of the pistons to cause the pistons to recip-- rocate in the cylinders and to pumpliqui'd'when the rotors are rotated and are eccentric to each other. Pumps of this type are often employed in pump due to a number of small factors including liquid which passes across the face of the pump valve from the discharge port tothe intake po'r't, liquid which leaks out of the valve, liquid which escapes past the pump cylindersand distortion of parts of the pump due to creationof pressure. The difference between the displacement of the pump and the volume of liquid actually discharged is known as the slip'of the pump; The pump ordinarily is connected to a hydraulic motor which also has slip and there may be slip in the channels which connect the pump -to the motor. The difference betweenthe pump displacement and the volume ofliquidactually consumed in driving the motor'is known-as-=the slip of the system. i

The slip is negligible when pumppressure is low and it increas'esas the-pump pressure in creases but the total slip at maximum pressure is only a very small percentage of themaximum volumetric capacity of the pump. Under certain conditions however, the rate at which a pump is required to deliver liquid may be no higher-than the rate of slip when pump pressure is maximum. For example, a machine tool provided with a feed pump must often be' adjusted to feed the tools into a workpiece at such a slow rate that the rate at which the pump must deliver liquid to produce that slow feed rate is less thanthe rate of slip when pump pressure is maximum. Ordinarily a moderate pressure is required to fee'd'the' tool into the workpiece but, if the stock being removed should increase in thicknes's or if the tool should strike a hard spot-in the'metal as Often happens, P mp pressure would rise sub stantially with a corresponding increase'in slip. Consequently, unless means were provided-to compensatefor variations in slip, the: increase in slip would-cause the feed-rate todecreasesomuch 2 thatthe workpiece when finished wouldbe unsatisfactory. r

Various means forcompensating for slip-have he'retofor been proposed but. all of the; prior means are inaccurate, too expensive or too large and cumbersome for many installationsg.-

The present invention has asan objecttopro vide a pump which will accurately, simply and inexpensively compensate for variations in slip due -'to variations in pressure.

The cylinder barrel ordinarily is mounted upon the 'pintle' with a very close running fit'in order to keep the-slip to a minimum and thisarrangementvery satisfactory under most conditions but under-certainconditions the cylinder barrelwill 'sei'ze upon the pin-tle.

A pump constructed according tO the-p-rsent inventio'nhas the advantagethat it may have a greater clearance between the cylinder barrel and the "pintle' and thereby avoid or greatly reduc the danger of seizure.

Other objects and advantages will appear from the following description of the embodimentsof the invention shown in the accompanying drawings in which the views are as follows:

Fig. l'is a front view-of a well knowntype-of pump in which the invention is embodied; the frame of the pump having been omitted to sim' plify the view.v i

.is a longitudinal section partly in full takenionthe slightly irregular linei2-'- 2 of Fig.1 and. showing parts of the pump frame.

Fig.3 is a transversesection takenon thellne 3 c 4 is a transverse section'partly in full taken on the lined-4 of Fig. 2 but showing the rotors, rotated to a position difierentfromthat shownjin I Fig. 5 is onlyon the line 4-4 of Fig. 2 but drawn toa larger scale.

Fig, 6 is a vertical longitudinal section through another well known type of pump in which the inventionis embodied, certain parts of the pump having been-omittedto simplify the view.

Fig. 7 is a transverse section takenon the line l-l of Fig. -6. I V 1 I Thepumps have been shownwith the mace thereof-arranged horizontallyso thatthe rotors rotate in a vertical plane and they will be so described herei'nbut itis to be understood that theterms used herein to designate positions a'n'd directions refer to the drawings only and lnfno way limit the invention as the pump may be mounted in diflerentpositions.

Figs. 1=5

a section taken through the, pint'le cylinder barrel is arranged within outer rotor l and is journalecl upon a valve shaft or pintle 6 which is supported in the same horizontal plane as shaft 2 by a pintle support or pendulum I. Pintle 6 has one end portion thereof fixed within the lower portion of pendulum 'l and it is accurately located therein by a key 8. The upper portion of pendulum I is journaled upon a stationary shaft 9 which has the end portions thereof supported in portions of frame 3. The arrangement is such that pendulum I may be rocked upon shaft 9 to vary the displacement of the pump between zero and maximum as will presently be explained.

Shaft 9 has formed therein two passages and H which extend radially inward in the plane of pendulum I and have been shown as extending axially from that plane through the front end of shaft 9 and as communicating, respectively, with two pipes 12 and I3 through which liquid fiows to and from the pump. The radial ends-of-passages l0 and II register, respectively, with two passages l4 and I5 which are formed in pendulum T andareconnected, respectively, by two pipes 'lfi and if. to two other passages l8 and i9 which are formed in pendulum 1 above and below pintle 5. Pendulum 1 is rocked through such a small angular distance in adjusting pump displacement from zero to maximum that passages l4 and I5 remain nearly in complete registry with passages l0 and H respectively.

Passages l8 and I9 register, respectively, with two passages and 2| which extend therefrom radially into pintle 6, and then extend axially thereof into communication withtwo ports 22 and 23 which extend radially inward from the peripheral surface of pintle 6. The unbroken portions of the pintle surface between the adjacent ends of ports 22 and 23 constitute bridges which have been designated in Figs. 4 and 5 by the reference numerals 24 and 25. The inner rotor or cylinder barrel 5 has a plurality of equally spaced radial cylinders 26 formed therein, five being shown, and a cylinder port 2'! extending through the inner end of each cylinder to communicate with pintle ports 22 and 23 alternately as cylinder barrel 5 rotates upon pintle 6. Each cylinder has fitted therein a piston 28 which has been shown in Fig. 4 as including a hollow piston shell 29 which is closely fitted in cylinder 26 and a push rod 30 which is loosely fitted in shell 29 and is provided at its outer end with a crosshead 3| which is normal to the push rod axis. The inner face of each crosshead 3| rides upon two aligned surfaces 32 which are formed upon outer rotor l at right angles to a radius thereof. The outer face of each crosshead 3| engages a roller bearing 33 which rides upon a wear plate 34 arranged parallel to the adjacent surface 32 and fixed to outer rotor I. It will be obvious that, when the axis of pintle 6 and rotor 5 is offset toward the right from the axis of rotor l as shown and rotors I and 5 are rotated in a clockwise direction as indicated by the arrow on Fig. 4 the pistons 28 in the lower half of rotor 5 will move progressively outward and will draw liquid into their cylinders through ports 21 and 23, passages 2| and I9, pipe I! and passages I5 and II from pipe l3 and the pistons 28 in the upper half of rotor 5 will be forced progressively inward by outer rotor l and will eject liquid from their cylinders through ports 21 and 22, passages 20 and I8, pipe 16 and passages l4 and [0 into pipe l2 at a rate determined ;by the speed of the rotors and the distance that the axis of pintle 5 is offset from the axis of rotor I. When the axis of pintle 6 is offset toward the left from the axis of rotor I, the flow of liquid will be reversed. When the axes of pintle 6 and rotor l coincide, no reciprocation of the piston will occur and pump displacement will be zero.

While pintle 6 and the bore in cylinder barrel 5 have been shown as being straight, they are tapered in practice but the taper is so slight that it could not be shown in the drawing. Cylinder barrel 5 is prevented from moving rearward by rotor l and is prevented from moving forward by a shim or shims 35 arranged between its front end and pendulum l and of such thickness as to establish the proper running clearance between cylinder barrel 5 and pintle 6. Pendulum 'l is accurately located upon shaft 9 by shims 36 and 31 arranged between its ends and the adjacent portions of frame 3.

With the exception of the details of the bridges 24 and 25 on pintle 6, the pump as thus far described is substantially the same as the pump shown in Patent No. 1,753,562,

In the prior pump, the centerline of the bridges is on the horizontal centerline ofthe pintle and the circumferential length of each bridge ordinarily is slightly greater than the diameter of the cylinder ports to provide a positive seal between the two cylinder ports. According to the present invention and as shown in Fig. 5, the centerline of bridges 24 and 25 is rotated from the horizontal centerline of pintle 6 through a small angular distance in a direction opposite to the direction of rotation of the rotors and the circumferential length of each of bridges 24 and 25 is no greater than the diameter of a cylinder port 21.

Preferably, the ends of pintle ports 22 and 23 are arcuate as shown in Fig. 6 in which case the circumferential length of each bridge may be slightly less than the diameter of a cylinder port so that a cylinder port begins to open to one pintle port just as it moves out of communication with the other pintle port. The diameter of the cylinder port is so little greater than the length of a bridge and the cylinder barrel rotates so fast that there is substantially no flow of liquid from the high pressure pintle port to the low pressure pintle port as a cylinder port crosses a bridge but the arrangement provides quiet operation of the pump.

The forces exerted by the outer rotor upon the pistons to move them inward and to create pressure in the liquid are known as pumping forces. When the pump is adjusted as shown and is discharging liquid under pressure into pintle port 22, the pumping force exerted upon a piston will be transmitted through the liquid to pintle 6 as soon as the port 21 of the cylinder containing that piston opens to port 22 and the force will continue to act upon pintle 6 until that cylinder port opens to pintle port 23. The pumping force will act directly downward upon pintle 6 when the cylinder is on the vertical centerline of the pintle andit will act upon pintle 6 at-an angle to the'vertical centerline thereof when the cylinder is at either side of that centerline. The forces acting upon the pintle at the left of its vertical centerline are resolved into vertical components which tend to move the pintle downward and into horizontal components which tend to move the pintle toward'the right and the forces acting upon the pintle at the right of its vertical centerline are resolved into vertical components which tend to-move the pintle downward and horizontal components which tend to move the pintle toward the left.

If the centerline of the bridges were on the horizontal centerline of the pintle as in the prior pumps and if the length of each bridge did not exceed the diameter of the cylinder port, the

horizontal components of the forces acting upon the pintle at one side of its vertical centerline would be substantially equal to the horizontal components of the forces acting upon the pintle at the other side of its vertical centerline so that there would be substantially no net force tending'to move the pintle horizontally.

With the centerline of the bridges rotated from the horizontal centerline of the pintle through a small angular distance in a direction opposite to the direction of rotation of the rotor as indicated in Fig. 5, a cylinder in passing from one pintle port to the other pintle port opens to that other pintle portbefore the centerline of the cylinder crosses the horizontal centerline of the pintle. As soon as a cylinder port opens to the high pressure pintle port, a pumping force is transmitted through the liquid in that cylinder to the pintle and, as soon as a cylinder opens to the low' pressure pintle port, the pumping force which had been transmitted to the pintle is destroyed. Consequently, the horizontal components of the pumping forces which urge the pintle in a direction to increase pump displacement exceed the horizontal components of the pumping forces which urge the pintle in a direction to decrease pump displacement.

For example, the port 27 of a cylinder passing acro'ss bridge 24 (Fig. 5) will open to pressure port 22 before the centerline of that cylinder passes across the horizontal centerline of the pin tle and the port 2'! of a cylinder passing across bridge will open to suction port 23 before the centerline of that cylinder passes across the horizontal centerline of the pintle. Therefore, pintle 6 is subjected to pumping forces through a greater angular distance at the left of its vertical centerline than at the right thereof and, consequently, the horizontal components which urge pintle 6 toward the right or in a direction to increase pump displacement exceed the horizontal components which urge pintle 6 toward the left or in a direction to decrease pump displacement. The preponderance of force urging the pintle in a direction to increase pump displacement is utilized in compensating for variations in slip due to variations in pressure as will presently be explained. V

The mechanism for swinging pendulum 7 upon shaft 9 to thereby vary pump displacement includes a spring arm which is rigidly secured to pendulum I. As shown, spring arm #95 is formed integral with an arm or link 46 which is fixed to pendulum I as by means of an extension 41 on pintle 6 and a bolt 48 both of which are closely fitted in link 46 and have suitable nuts on the outer ends thereof.

Spring arm 45 is provided at its lower end'wi-th an abutment which: hasbeen shown asi'being a.

roller-"49 mounted upon a shaft 50 and in engage-- ment with a control element which has been shown as being a cam 5| mounted upon a control shaft-52. Roller '49 is held in contactwith.

cam 5| by a spring53 which tends to swing pen;- dulum 1 toward the left. As shown, spring53 has'one of its ends connected to a rigid arm 54. which is formed integral with link. 46 and; its: otherend connected to an adjusting bolt 55.

carried by a stationary support 56.

Spring arm 45 and spring 53 are so calibrated that spring 53 will positively hold abutment 49 in contact" with control camv 5| at all adjustments of -the:pump and, when. the pump is. adjusted to discharge liquid into pipe 12 as previously ex-, plained; spring 53 will flex spring arm as showmwhenpump pressure is zero and spring arm 35 will have sufiicient strength to swing pendulum iin a directionto increase pump dis placement when it is aided-by the horizontal. componentsof the pumping forces.

With the pump adjusted as shown, it will discharge liquid at a predetermined rate according 6. a slight distance toward the right and thereby increase pump displacement. Since the pumping forces are proportional to pump pressure, the horizontal components thereof are likewise pro portional to pump pressure and, since the slip varies nearly in proportion to. variations in pressure, the tension of spring 53 may be so adjusted by adjusting bolt 55 that pump displacement is increased by an amount substantially equal tothe increase in slip due to the increase in pressure so that pump delivery remains substantially at the rate determined by the adjustment of earn 5! If thereafter pump pressure should decrease; the horizontal components of the pumping forces would' correspondingly decrease and permit spring 53 to correspondingly decrease pump displacement.

If cam 5! were rotated through a suiiicient angular distance to permit spring 53 to swing pendulum '1 far enough to move the axis of pintle 5 to the left ofthe axis of outer rotor I, the pump would discharge liquid in the opposite direction and spring arm 45 would not deflect when pump pressure was zero. When the pump created pressure; the horizontal components of the pumping force. would'urgepintle 6 toward the left and the force exerted upon the pintle by the horizontal, components of the pumping forces together with theforce exerted by spring 53 would cause spring arm 45 to flex and permit pintlet to move toward the left to increase pump displacement and thereby compensate for the slip caused by the increase in pressure as explained above.

It previously has been pointed out that in prior feed pumps of this type the cylinder barrel ordinarily is mounted upon the pintle with a very close running fit in order to keep the slip; at a minimum and that under certain conditions the cylinder barrel will seize upon the pintle.

Whenthe temperature of the cylinder barrel is. low and pump pressure suddenly increases, the'heatgenerated due to the increase in pressure and to shearing the film of liquid between the cylinder barrel and the pintle causes the aesacse 7 metal adjacent to the mating surfaces of the cylinder barrel and the pintle to expand before the rest of the metal in the cylinder barrel becomes heated. Consequently, the heated metal of the cylinder barrel expands inward and reduces the running clearance. If the cylinder barrel has a close running fit upon the pintle as in the prior pumps, this reduction in the clearance will occasionally cause the cylinder barrel to seize upon the pintle, particularly if there are particles of foreign matter in the motive liquid.

Since a pump constructed according to the present invention automatically compensates for variations in slip due to variations in pressure, it is not necessary to keep the slip at the lowest possible minimum and the cylinder barrel may be fitted upon the pintle with sufiicient clearance to avoid substantially all danger of seizure.

In the pump shown in Figs. 1-5 the outer rotor rotates on a stationary axis and the pintle is moved to vary pump displacement but the invention is also applicable to a pump in which the pintle is stationary and the outer rotor is moved to vary pump displacement.

Figs. 6 and 7 The pump shown in these figures is also a well known type and, except that the pistons and cylinders have been shown as being on radii of the cylinder barrel instead of being inclined to those radii, the pump is similar to the pump shown in Patent No. 2,105,454 to which reference may be had for details of construction. Consequently, only so much of the pump has been shown as is necessary to illustrate the application of the invention thereto.

The pump has an inner rotor or cylinder barrel 6| journaled upon a valve shaft or pintle 62 which is rigidly supported in a stationary position by having one end portion thereof fixed in a portion of the pump frame or case 63 only portions of which have been shown.

The portion of pintle 62 upon which cylinder barrel 6| is journaled is substantially the same as the corresponding portion of pintle 6 shown in Figs. 2-5. That is, it has two diametrically opposed pintle ports 64 and 65, which correspond to ports 22 and 23, and the unbroken surface of the pintle between adjacent ends of the pintle ports constitute bridges 68 and 61 which correspond to bridges 24 and 25 and have the centerline thereof rotated through a short angular distance from the horizontal centerline of the pintle in a direction opposite to the direction of rotation of cylinder barrel 6|. Pintle 62 has formed therein two passages 68 and 69 which extend axially rearward from ports 64 and 65. respectively, and then extend radialll outward into communication, respectively, with two passages 10 and 1| which are formed in case 63 and are adapted to be connected, respectively, to a hydraulic circuit as by means of pipes 12 and I3.

Cylinder barrel 6| has formed therein a plurality of radial cylinders 14 and an equal number of cylinder ports 15 each of which extends through the inner end wall of a cylinder andis adapted to register with pintle ports64 and G5 alternately as cylinder barrel 6| rotates. Rotation of cylinder barrel 6| is effected by a drive shaft 16 which is connected thereto by a coupling 11. Shaft 16 is journaled in suitable bearings (not shown) and preferably is also journaled in the end of pintle 62 as indicated in dotted lines in Fig. 6.

A piston 18 is closely fitted for reciprocation in each cylinder 14 and it has its outer end beveled to engage a beveled reaction surface 18 carried by an outer rotor 88 which is arranged within a hollow support or slide block 8| and is 5 rotatably supported therefrom by two bearings 82 and 83.

Slide block 8| has fixed to the top and bottom thereof four wear plates 84 each of which engages a wear plate 85 which is fixed to case 63. The rear end of slide block 8| engages the rear wall of case 63 and the front end thereof engages a partition plate 86 which is fixed in case 83 near the front end thereof. The arrangement is such that slide block 8| is prevented from moving vertically or axially of pintle 62 but it may be moved transversely of pintle 62 to vary pump displacement.

As shown, slide block 8| is urged toward the right by a spring 8'! and it is adapted to be moved toward the left by a link or arm 88 which is pivoted intermediate its ends upon a bolt 89 carried by lug 90 which is fastened to slide block 8|. Arm 88 is journaled at its upper end upon a bolt 9| carried by case 63 and its lower portion is formed into a spring arm 92 which carries at its lower end an abutment shown as being a roller 93 journaled upon a bolt 94. Roller 93 is engaged by a control element shown as being a cam 95 fixed upon a control shaft 96.

When cam 95 is adjusted to move slide block 8| toward the left until the axis of outer rotor 80 is at the left of the axis of pintle 62 as shown in Fig. 7 and rotor 6| is rotated clockwise as indicated by the arrow on Fig. 7, the pistons 18 in the lower half of cylinder barrel 6| will move progressively outward, the pistons i 8 in the upper half of cylinder barrel 6| will be forced progressively inward by outer rotor 88, liquid will flow from pipe 13 through passages II and 69 and ports 65 and 15 into the cylinders containing outward moving pistons and the inward moving pistons will force liquid from their cylinders through ports 15 and 64 and passages 68 and 10 into pipe 12. If the axis of outer rotor 80 were at the right of the pintle axis, the flow of liquid would be reversed. When slide block 8| is in its neutral position in which the axis of rotor 80 coincides with the pintle axis, no reciprocation of the pistons will occur and pump displacement will be zero.

When the pump is creating pressure, the horizontal components of the pumping forces tend to effect relative movement between the pintle and the outer rotor. In the pump shown in Figs.

1-5, the outer rotor cannot be moved horizontally and the horizontal components of the pumping forces tend to move the pintle. In the pump shown in Figs. 6 and '7, pintle 62 is fixed and the horizontal components of the pumping forces tend to move outer rotor 80 and slide block 8| which supports it.

With slide block 8| at the left of its neutral position as shown and with the pump discharging liquid under pressure into pipe 12, the horizontal components of the pumping forces at the left of the vertical centerline of pintle 62 will tend to move slide block 8| toward the left and the horizontal components of the pumping forces at the right of the vertical centerline of pintle 62 will tend to move slide block 8| toward the right. Since the centerline of bridges 66 and 61 is rotated a short angular distance from the horizontal centerline of the pintle in a direction opposite to the direction of rotation of the rotors, the horizontal components of the pumpplus the force exerted by-spring 1 ing forces atthe left, of; the vertical; centerline -,of the pintle will exceed-the horizontal comflexed as shown when slide block Bl is moved toward the left beyond'itsneutral position and pump pressure is zero. 'When pump pressure rises, the horizontal components of the pump-r. ing forces will urge slide block 8| toward the left and the force thus exerted upon slide block 8| arm 92 overcomes the resistance of spring 81 suiiiciently to move slide block 8! enough farther toward them left to increase pump displacement sufiiciently to compensate forthe increase in slip. due to. the increase in pressureas previouslyvexplained in connection with the;;description of the pump shown in Figs. 1-5.

The invention disclosed herein is susceptible of other modifications and adaptations without departing from the scope of theinvention which is hereby claimed as follows.

Iclaim:

1. A pump comprising an outer rotor rotatable in a vertical plane, asupport for said rotor, a pintle extending into said outer rotor and provided with diametrically opposed intake and discharge ports and with-axial passages communicating with said ports, the adjacent ends of said ports being separated from each other by unbroken portions of the peripheral surface of said pintle which constitute-bridges toprovide seals between said ports, an inner rotor journaled upon said pintle and provided with a plurality of equally spaced radial cylindersand withanequal number of cylinder ports each of which extends through the inner end wall of a cylinder to communicate with said pintle ports. alternately as said inner rotor rotates, a support for .saidpintle, one of said supports being movable in respect to the other support to move :one of said rotors between a position in which the axes of said rotors are coincidentandthei displacement of said "pure to zero and a positioninwhich --th e-;axes, ofsaid rotors areoifset from-each other and the displacement ofv said'pump is maximum, a piston fitted in each ofsaidcylinders, and having the outer end thereof in engagement with said outer rotor, means forrotatingone ofsaid-rotors, rota tion of one rotorcausing. rotation of, the other rotor due to engagement of said pistons with said outer rotor and. also causing said pistons to r ciprocate in said cylinderssand to pump s when the axes of said rotorsare offset from each other, a control arm-connected to one of said supports, a spring arm fixed to said control arm, an abutment carried by the free end of said spring arm, a control element normally engaging abutment-and-adjustable tomove said arm in a direction to increase pump displacement, and a spring to urge said movable support in the opp-o site direction and to hold said abutment in engagement with said control element, saidpi t e bridges being rotatedthrough a small anguzar distance from thehor-izontal centerline of said pintle in a direction opposite to-the direction of rotation of said rotors tothereby cause "horizontal components of thepumping. forces to urge said pintle toward its maximumdisplacement position. ,2. A pump comprising an outer rotor rotatable in a vertical plane, a support for said rotor; a

pintle extending into said outer rotor and provided with diametrically opposed intake and discharge ports and with axial passages communicating with said ports, the adjacent ends of said ports being separated from each other by unbroken portions of theperipheral surface of said pintle which constitute bridgestoprov-ide seals between said ports, an inner rotor journaled upon said pintle and provided with a plurality of equally spaced radial cylinders and with an equal number of cylinder ports each of which extends through the inner end wall of a cylinder to communicate with said pintle ports alternately as said inner rotor rotates, a support for said pintle,

one of said supports being movable in respect to the other support to move one of said rotors between a position in which the axes of said rotors are coincident and the displacement of said pump is zero and a position in which the axes of said rotors are oiTset from each other and the displacement of said pump is maximum, a piston fitted in each of said cylinders and having the outer end thereof in engagement with said outer rotor, means for rotating one of .said rotors, rotation of one rotor causing rotation of the other rotor due to engagement of said pistons with said outer rotor and also causing said pistons to-reciprocate in said cylinders and to pump liquid when the axes of said rotors are offset from each other, a control arm having one portion thereof connected to said movable support and another portion thereof divided into a rigid arm and a spring arm, an abutment carried by the free end of said spring arm, a control element normally engaging said abutment and adjustable to move said arm in a direction to increase pump displacement, and a spring connected to said rigid arm to urge said pintle support in the opposite direction and to hold said abutment against said control element, said pintle bridges being rotated through a small angular distance from the horizontal centerline of said pintle in a direction opposite to the direction of rotation of said rotors tov thereby cause horizontal components of the pumping forces to urge said pintle toward its maximum displacement position. i

3. A pump according to claim 2 in which the angular. distance between the adjacent ends of said pintle ports is no greater than the angular length of said cylinder ports. 4. A pump comprising an outer rotor rotatable in a vertical plane, means for rotating said rotor, a pintle extending into said outer rotor and provided with diametrically opposed intake and discharge ports and with axial passages communicating with said ports, the adjacent ends of said ports being separated from each other by unbroken portions of the peripheral surface-of said pintle which constitute bridges to provide-seals between said ports, an inner rotor journaled upon said pintle and provided with a plurality of equally spaced radial cylinders and with an equal numberof cylinder ports each of which extends through the inner end wall of a cylinder to communicate with said pintle ports alternately as said inner rotor rotates, a piston fitted ineach cylinder, means for transmitting motion from said outer rotor to said pistons to thereby cause axis of said outer rotor, a support for said pintle movable horizontally between a position in which the axis of said pintle coincides with the axis of said outer rotor and the displacement of said pump is zero and a position in which the axis of said pintle is offset from the axis of said outer rotor and the displacement of said pump is maximum, a spring arm having one end portion thereof fixed to said pintle support, an abutment carried by the free end of said spring arm,

a control element normally engaging said abutment and adjustable to move said arm and said pintle in a direction to increase pump displacement, and a spring to urge said pintle support in the opposite direction and to hold said abutment in engagement with said control element, said pintle bridges being rotated through a small angular distance from the horizontal centerline of said pintle in a direction opposite to the direction of rotation of said rotors to thereby cause horizontal components of the pumping forces to urge said pintle toward its maximum displacement position.

5. A pump according to claim 4 in which the angular distance between the adjacent ends of said pintle ports is no greater than the angular length of said cylinder ports.

6. A pump comprising an outer rotor rotatable in a vertical plane, means for rotating said rotor, a pintle extendin into said outer rotor and provided with diametrically opposed intake and discharge ports and with axial passages communicating with said ports, the adjacent ends of said ports being separated from each other by unbroken portions of the peripheral surface of said pintle which constitute bridges to provide seals between said ports, an inner rotor journaled upon said pintle and provided with a plurality of equally spaced radial cylinders and with an equal number of cylinder ports each of which extends through the inner end wall of a cylinder to communicate with said pintle ports alternately as said inner rotor rotates, a piston fitted in each cylinder, means for transmitting motion from said outer rotor to said pistons to thereby cause said inner rotor to rotate in unison with said outer rotor and also to cause said pistons to reciprocate in their cylinders and to pump liquid when the axis of said pintle is ofiset from the axis of said outer rotor, a support for said pintle movable horizontally between a position in which the axis of said pintle coincides with the axis of said outer rotor and the displacement of said pump is zero and a position in which the axis of said pintle is offset from the axis of said outer rotor and the displacement of said pump is maximum, a control arm having one end portion thereof fixed to said pintle support and the other portion thereof divided into a spring arm and a rigid arm, an abutment carried by the free end of said spring arm, a control element normally engaging said abutment and adjustable to move said arm and said pintle in a direction to increase pump displacement, and a spring connected to said rigid arm to urge said pintle support in the opposite direction and to hold said abutment against said control element, said pintle bridges being rotated through a small angular distance from the horizontal centerline of said pintle in a direction opposite to the direction of rotation of said rotors to thereby cause horizontal components of the pumping forces to urge said pintle toward its maximum displacement position.

7. A pump according to claim 6 in which the 12 angular distance between the adjacent ends of said pintle ports is no greater than the angular length of said cylinder ports.

8. A pump comprising an outer rotor rotatable in a vertical plane, means for rotating said rotor, a pintle extending into said outer rotor and provided with diametrically opposed intake and discharge ports and with axial passages communicating with said ports, the adjacent ends of said ports being separated from each other by unbroken portions of the peripheral surface of said pintle which constitute bridges to provide seals between said ports, an inner rotor journaled upon said pintle and provided with a plurality of equally spaced radial cylinders and with an equal number of cylinder ports each of which extends through the inner end Wall of a cylinder to communicate with said pintle ports alternately as said inner rotor rotates, a piston fitted in each cylinder, means for transmitting motion from said outer rotor to said pistons to thereby cause said inner rotor to rotate in unison with said outer rotor and also to cause said pistons to reciprocate in their cylinders and to pump liquid when the axis of said pintle is offset from the axis of said outer rotor, a shaft arranged in a stationary position above said outer rotor and provided with passages for connection to an external circuit, a pendulum having the upper end portion thereof journaled upon said shaft and having said pintle fixed in the lower end portion thereof to thereby support said pintle and said inner rotor, said pendulum being swingable upon said shaft to move said pintle between a position in which the axis of said pintle coincides with the axis of said outer rotor and the displacement of said pump is zero and a position in which the axis of said pintle is offset from the axis of said outer rotor and the displacement of said pump is maximum, a control arm having one end portion thereof fixed to said pendulum and the other portion thereof divided into a spring arm and a rigid arm, an abutment carried by the free end of said spring arm, a control element normally engaging said abutment and adjustable to move said arm and said pintle in a direction to increase pump displacement, and a spring connected to said rigid arm to urge said pintle support in the opposite direction and to hold said abutment against said control element, said pintle bridges being rotated through a small angular distance from the horizontal centerline of said pintle in a direction opposite to the direction of rotation of said rotors to thereby cause horizontal components of the pumping forces to urge said pintle toward its maximum displacement position.

9. A pump according to claim 8 in which the angular distance between the adjacent ends of said pintle ports is no greater than the angular length of said cylinder ports.

JAMES K. DOUGLAS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,753,562 Ferris Apr. 8, 1930 2,105,454 Ferris Jan. 11, 1938 2,431,176 Hoifer Nov. 18, 1947 2,496,915 Hoffer Feb. '7, 1950 2,529,309 Purcell Nov. 7, 1950 

